There are numerous devices and processes where the presence of hydrogen is undesirable. One example is the insulated-anulus steel tubing that is used for steam injection for secondary oil recovery. It is desired, for thermal insulation purposes, that the anulus consist of either a vacuum or an inert gas such as argon. Hydrogen can enter the insulating anulus as a result of outgasing from the steel or external corrosion processes, thus decreasing the insulating ability of the anulus. Another example is the ammonia heat pipe which can suffer impaired operation from the buildup of hydrogen resulting from internal corrosion processes. Another series of examples are numerous inert gas chambers, such as "dryboxes", which are used widely in laboratories and industry. These chambers may, at times, be undesirably contaminated with hydrogen or the heavy isotopes deuterium and tritium. Yet another example is the separation of small amounts of hydrogen from helium during the commercial isolation of helium. There are numerous other examples where it is desirable to getter hydrogen or its isotopes from vacuum chambers or various gasses.
Numerous examples of the use of hydrogen getters can be found but each has certain disadvantages. Titanium metal has been used but it must be heated to at least 600.degree. C. to render it active to hydrogen absorption and can easily be de-activated by the presence of gaseous impurities such as oxygen or water. Furthermore, once saturated with hydrogen, titanium must be heated to the order of 600.degree. C. under vacuum to remove the hydrogen and make it capable of reuse.
Another hydrogen getter that has often been used is depleted uranium metal. One disadvantage of uranium is that it forms a fine power upon hydriding, usually rendering it potentially pyrophoric upon exposure to air. A further disadvantage of uranium, even in the U-235 depleted form, is the fact that it is mildly radioactive, requiring special handling and disposal.
A series of zirconium-based getters are sold commercially by SAES Getters of Milan, Italy. These consist of at least 70% by weight of zirconium, with the balance consisting of elements such as aluminum, vanadium, iron and nickel. While these commercial getters have been used widely and successfully for hydrogen gettering, they also have a number of undesirable drawbacks. First of all they require temperatures in the range of 200.degree.-900.degree. C. for activation. They will generally not getter hydrogen at room temperature without activation. Second, once activated with hydrogen, they must be heated under vacuum to temperatures on the order of 800.degree. C. to thoroughly remove the hydrogen so that they can be reused as hydrogen getters. Third, because of their high zirconium content, they cannot be melted in readily available air furnaces or common ceramic crucibles but rather must be vacuum arc melted in a water-cooled copper crucible, an inherently more expensive process than air melting in a ceramic crucible.
In the article, "The System Zirconium-Nickel and Hydrogen", by G. G. Libowitz, et al. in Journal of Physical Chemistry, Vol 62 (1958) pp. 76-79, the hydrogen absorption and desorption properties of an intermetallic compound ZrNi (60.8 wt. % Zr--39.2 wt. % Ni) were first described. This compound has attractive properties for many reusable hydrogen getter applications. However, no data below 100.degree. C. was presented and, in fact, this material has undesirable sluggish activation properties at room temperature.